TortoiseSVN is a fairly well recognised SVN handling program.
SVN is a way of managing source code, considered obsolete by some but with a massive long and popular history never the less ( https://sourceforge.net/ used it for many years, still offers it even). That is then a program some use to keep up to date with any changes to the code and also possibly send it back in.
You probably would have got it if some open source program wanted you to compile something to have it run (or have a modded version of something like that) and said you need a SVN checkout or something.
If you are on Linux playing programmer that is a good way of doing it, if you are just playing person that can follow a guide on a Windows computer then overkill). Though unless you want to always be getting updates (or contributing to it) then most services will offer a nice zip of the current code or whatever you can feed to your compiler.